Seperate Heat Exchanger For Herms

[jfinney]

Hi there guys,

I am keen to build a HERMS system with a seperate heat exchanger, could someone pleas advise on whether I should use a 7 or 10 litre vessle and if the efficiencies and performance varies? I was thinking of using a small esky cooler like the one pictured below (7.6 litre), do you think this would perform better than a pot, given it is built for thermal efficiency?

I would love some advice, as tried to add this question to an existing HERMS discussion, but it was ignored! Sorry, but I am new to this forum, but not to brewing!

 

[roller997]

In the HERMS thread, there was a picture of a rather clever way to insulate metal pots - The idea was to sit the pot in a larger plastic pot (a fermenter was used for this one) and to fill it with the insulation foam so it is covered all the way around. As the insulation foam was probably 2-3 times thicker than the Esky cooler you have depicted here I would think it would provide even better insulation properties. If you use enough electrical power for your Heat Exchange then it may not make that much of a difference I would think, especially if you look at a small vessel like 7-10 liters.

Cheers

Roller

 

[razz]

You obviously didn't care for my response in the other thread jfinney?
Just for the record, I think that esky type container will eventually give up due to the amount of heat it will absorb. I've done the same thing with a largewr version and after many years it has cracked. Get at least 3 meters of 1/2 inch copper and make a coil, then look for a small s/s pot that it will fit into. I think going through the lid is a good way to go. There are a few pictured on the forums, just have a good look through the equipment threads.

 

[Sammus]

small there better, and you dont even need insulation on a herms.

 

[roller997]

I bought an aluminium pressure cooker which is VERY solid and was only $49 Buy it now at the time on Fleabay a month or so ago.

Here is an identical aluminium pressure cooker at a slightly higher price
http://cgi.ebay.com.au/New-7Litre-Spanish-...=item563b62e4bf

My intent was to use the rather sturdy lid to mount the copper lines as the lid is very solid (as it has to be for a pressure cooker). Once I have mounted elements through the bottom, I will insulate it similar to what the other chap did with a big bucket and some insulation foam.
I am sure at some Op Shop or at a market you can get a pressure cooker for less than $20 if the new one is too expensive.

I did have concerns that plastic which is made for keeping cold or semi warm foods in it would not be all that tolerant to the high temperature ranges, however I had no evidence to base that concern on. It looks like Razz has provided some solid evidence which would make me less likely to ever consider a small plastic vessel for a HE, considering the fact that you can insulate a metal vessel and the heat you loose is not very significant when compared to the energy your elements should dissipate.


Cheers

Roller

 

[TidalPete]

small there better, and you dont even need insulation on a herms.

+1

Even though my HE is insulated I've found that there was actually no need to insulate it in the first place.
Get a 7 litre pot & cram in all the copper tubing you can.

T

 

[egolds77]

I run a HERMS with my heat exchange pot uninsulated and it works great. My thinking was it has better control over the heating without the potential of major overtemps due to the thermal insulation.
I should buy some thermal mating and temp fit it around my HX and see how it effects its performance to prove or disprove my assumptions.

I'd go with the 7L pot and put as much copper coil in there as you can. I think the pot I have for my HX is a 9L from Big W with a 2000-2200W kettle element in it and about 5.5m of copper coil. I get a temp ramping of about 1.5 degrees C /min. The smaller the vessel the quicker the response to heat input and the more copper coil you can stuff in there the more efficent it will be with transfering heat to the mash flowing through. If you are wanting to ramp the temperature of the mash using the heat exhanger then you will get a greater temperature increase / min with more copper coil per heating wattage.

ie Length of copper (m) x heating (watts) / volume (L) = rate of temp change (degrees C) / min

The volume (L) would not neccessarily be linear in its influence on the overall system as a larger volume holds more latent heat, less effected by the cooler mash, but it takes longer to increase by 1 degree C for the same heating power.

 

[mika]

Maybe a question for the other HERMS thread, but has anyone considered stirring the HEx vesse; to avoid stratification ? I know my HLT is very prone to this, but then it's a small horizontally mounted element in a 50L stainless vessel.

 

[egolds77]

Morebeer in the states sell a twisted copper coil which is designed to swirl the wort as it flows through, providing better heat distribution through the liquid. A motorised stirrer in boththe HX and HLT would help even heat distribution throughout for sure. I found a couple of very slow rpm motors from a microwave turn table, just haven't got around to making some stirrers.

 

[absinthe]

my exchanger is a round esky, about the same size as the one you are looking at.. i dont have any over run problems (you should never have overrun if you have a properly setup PID in fact the insulation should help make over run less likely as the ambient air temp wont have as much effect on the HE)and i have a small induction motor to stir the water in the exchanger, and i can just manage 1C (maybe a little less) a minute with a 1500W element but i do want to go to a 2400W

 

[dent]

Would it be a bit awkward to mount the heating element in that little esky?

I've posted this before, but I still like it:

(upgraded to a real table since then)

Temperature 'leakage' is not be an issue unless you're running the tubes through an ice bath or something. Even then it would still work. If you consider how much heat conduction you need to cool down several litres per minute of hot wort enough to matter (like when you try to get your chiller tap water colder, for instance), you'll see why. Your PID loop will also take care of the effects of any heat loss through kettle or tubing anyhow. I like this Pease PID for an explanation of PID operation, albeit from an electronics perspective.

Really this is pretty hard to screw up, the only critical thing I think is to ensure there is enough copper/stainless/whatever in your heat exchanger to ensure good conduction at your max flow rate.

 

[jfinney]

Thanks guys, guess I'll stick with the 7 litre pot, cram as much copper 1/2'' as possible in there, and attach in/out points to the lid. I guess stainless will look the part, and probably cheaper!